316L Yield Strength (Free Machining, Annealed 1.5" Bar)

[alexit]

I have been reviewing materials quoted from a variety of suppliers. With my drawing requiring 316L (Free Machining, Annealed 1.5" Bar) I have received certs indicating minimum yield strength of:
25ksi, 29ksi, 36ksi, 40ksi, 42ksi and 45ksi

How can the same 316L material be so different?

Am I not fully specifying the raw material? Are some of these not fully annealed? Are different suppliers manipulating carbon content? Nitrogen? Other additions not prohibited by the 316L spec?

Thanks for any input you might have!

 

[EdStainless]

-The spec only requires min Yield (25ksi) and min UTS and min elong, no maximums, and a max hardness.
The min Elong and max hardness are what keep them from offering material that is too strong.
-Nitrogen can be added at will, 316L and 316LN are the same alloy as far as the spec is concerned. It is the only element that you can deliberately add and not report.
-They will all be low C, but some will be 0.012% and some will be 0.030%, all within spec.

Also consider that Yield strength is a construct, not a true material property. I would wager that the UTS values are not as variable.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[TVP]

If the steel was sourced from multiple mills/heat treatment sources, then I would expect variation of yield strength within the range that you provided. The composition of 316L or 316LN has sufficient variation, together with the process variation that exists during annealing, that yield strength will easily vary by 50%.

 

[alexit]

Thanks everyone for your assistance!

Alex

 

[tbuelna]

alexit-

Per the question in your OP, I would not consider your material description (316L, free-machining, annealed, 1.5" bar) to be adequate for many situations. First, you should provide a material standard the 316L annealed bar should conform to. Second, you need to provide further definition of whether the "1.5" bar" is square or round. And one last minor point is that 316L is not normally considered to be a free-machining alloy. While it's lower carbon will make it machine slightly better than 316, it still does not machine anywhere near as readily as true free-machining stainless alloys like 203s or 303se.

 

[CoryPad]

Terry,

This sounds like Project 70 from Carpenter:

http://www.cartech.com/ssalloysprod.aspx?id=2830

 

[tbuelna]

I like how Carpenter's literature refers to Project 70 as being an "improved machining" version of conventional 316/316L alloys, as opposed to free-machining.

Unfortunately, the same thing that gives some stainless alloys their nice free-machining characteristics also makes them unsuitable for welding or for applications where fracture properties are a concern.

 

[EdStainless]

As I recall Outokumpu also make Prodec, which is an enhanced machining version of both 304L and 316L. The deal with Prodec is that it has as good of corrosion resistance as the base alloy, which isn't true for for the high S and Se grades.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[alexit]

tbuelna, the "bar" designation is an artifact of our ERP system - all materials received in lengths are designated "bar" = round, or "square" = square (there are other designations i.e. "hex", "strip" (thick x width), coil, tubing, etc.)

My understanding was free-machining 316 has a smaller grain structure than normal 316, a number of mills produce something like the Carpenter Project 70+ now with their "free machining" designation. Is this inaccurate?

Alex

 

[MikeHalloran]

Saying '316' and 'free machining' in reference to the same bar makes you look like a Supply Chain Manager.

That's not a compliment.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

alexit- In your OP you asked about 316L, which is a version of 316 typically used when welding is involved. The description "free machining" is totally subjective and has no specific meaning, and your purchasing dept would be free to claim any material they purchased that came anywhere close to a 316 alloy composition was acceptable. As CoryPad noted, Carpenter Project 70 is an alloy similar in composition to 316 having "improved machining" characteristics. But if you want your purchasing dept to procure Project 70, then that's what you need to clearly specify on your BOM.